Groundwater Arsenic Remediation

Treatment Technology and Scale UP
 
 
Elsevier Science (Verlag)
  • 1. Auflage
  • |
  • erschienen am 1. Januar 2015
  • |
  • 326 Seiten
 
E-Book | ePUB mit Adobe DRM | Systemvoraussetzungen
E-Book | PDF mit Adobe DRM | Systemvoraussetzungen
978-0-12-801377-9 (ISBN)
 

Arsenic abatement from groundwater in locations with a central water distribution system is relatively simple. The real challenge is selecting the most effective and affordable treatment and scale up option for locations which lack the appropriate infrastructure. Groundwater Arsenic Remediation: Treatment Technology and Scale UP provides the latest breakthrough groundwater treatment technologies and modeling and simulation methods for project scale up and eventually field deployment in locations which lack the proper central water distribution system to ensure arsenic free groundwater.


  • Covers the different removal methods, such as chemical, adsorption, separation by membranes, and membrane distillation
  • Includes the state-of-the-art modeling & simulation methods for optimization and field deployment
  • Provides economic and comparative analysis of each arsenic treatment technology
  • Englisch
  • Woburn
  • |
  • USA
  • 10,21 MB
978-0-12-801377-9 (9780128013779)
012801377X (012801377X)
weitere Ausgaben werden ermittelt
  • Front Cover
  • Groundwater Arsenic Remediation: Treatment Technology and Scale UP
  • Copyright
  • Dedication
  • Contents
  • Acknowledgements
  • Preface
  • Chapter 1: Introduction to the Arsenic Contamination Problem
  • 1.1. Arsenic chemistry
  • 1.2. Occurrence and causes of arsenic in groundwater
  • 1.3. Regulations and maximum contaminant level of arsenic
  • 1.4. Toxicity and health hazards
  • 1.5. Introduction to methods of arsenic removal
  • 1.5.1. Chemical Precipitation
  • 1.5.1.1. Alum Precipitation
  • 1.5.1.2. Iron Precipitation
  • 1.5.1.3. Lime Softening
  • 1.5.1.4. Coprecipitation
  • 1.5.2. Adsorption
  • 1.5.3. Ion Exchange
  • 1.5.4. Membrane Filtration
  • 1.5.4.1. Pressure-Driven Membrane Filtration
  • 1.5.5. Electrodialysis
  • 1.5.6. Temperature-Driven Membrane Filtration
  • 1.5.7. Hybrid Methods of Arsenic Removal
  • References
  • Chapter 2: Chemical Treatment Methods in Arsenic Removal
  • 2.1. Different forms of arsenic in groundwater
  • 2.2. Chemical precipitation
  • 2.2.1. Alum precipitation
  • 2.2.2. Lime softening
  • 2.2.3. Iron precipitation
  • 2.2.4. Enhanced coagulation
  • 2.2.5. Coprecipitation
  • 2.3. Physical separation
  • 2.3.1. Diffuse-double-layer theory
  • 2.3.2. Destabilization of colloids and settling of particles
  • 2.3.2.1. Double-layer compression
  • 2.3.2.2. Adsorption and neutralization of charge
  • 2.3.2.3. Enmeshment-precipitation
  • 2.3.2.4. Interparticle bridging
  • 2.3.3. Filtration
  • 2.3.3.1. Rapid sand filtration
  • 2.3.3.2. Backwashing
  • 2.4. Modeling and simulation of the physico-chemical processes for scaleup
  • 2.4.1. Introduction
  • 2.4.2. Operation of the treatment plant
  • 2.4.3. Measuring arsenic concentration in water
  • 2.4.4. Computation of percentage removal of arsenic
  • 2.4.5. Modeling and simulation of physico-chemical treatment process
  • 2.4.5.1. Process kinetics and modeling basis
  • 2.4.5.2. Modeling the process
  • 2.4.5.3. Material balance for the oxidizer unit
  • 2.4.5.4. Component mass balance of arsenic
  • 2.4.5.5. Component mass balance of oxidant
  • 2.4.5.6. Material balance of the coagulator and flocculator
  • 2.4.5.7. Material balance for the sedimentation unit
  • 2.4.5.8. Filtration Unit
  • 2.4.6. Determination of the model parameters
  • 2.4.6.1. Computation of flow rate and concentration of oxidant
  • 2.4.6.2. Computation of root mean square velocity gradient (G) in the coagulator/flocculator
  • 2.4.6.3. Computation of average flock size (dQM) in the coagulator-flocculator unit
  • 2.4.6.4. Computation of flow rate and concentration of coagulant
  • 2.4.6.5. Determination of settling velocity and superficial velocity in sedimentation unit
  • 2.4.6.6. Determination of the filtration pressure drops due to filter cake and filter medium
  • 2.4.6.7. Effects of the operating parameters
  • 2.4.6.8. Effect of pH
  • 2.4.6.9. Effect of oxidant dose
  • 2.4.6.10. Effect of coagulant dose
  • 2.4.6.11. Effect of feed concentration
  • 2.4.7. Performance of the system and the model
  • 2.5. Optimization and control of treatment plant operations
  • 2.5.1. Development of the optimization and control software
  • 2.5.2. The overall procedure of computation and output generation
  • 2.6. The numerical solution scheme and error monitoring
  • 2.6.1. Software description
  • 2.6.2. Software input
  • 2.6.3. Software output
  • 2.6.4. Running the software
  • 2.6.4.1. Software analysis
  • 2.7. Techno-economic feasibility analysis
  • Nomenclature
  • References
  • Chapter 3: Adsorption Method of Arsenic Separation from Water
  • 3.1. Introduction
  • 3.2. Adsorption kinetics
  • 3.3. Adsorbents used in arsenic removal
  • 3.3.1. Synthetic activated carbon-based adsorbents
  • 3.3.2. Metal-based adsorbents
  • 3.3.3. Performance of the adsorbents
  • 3.3.3.1. Activated carbon
  • 3.3.3.2. Activated alumina
  • 3.3.3.3. Zeolites
  • 3.3.3.4. Red mud
  • 3.3.3.5. Rice husk
  • 3.3.3.6. Fly ash
  • 3.3.3.7. Hematite and feldspar
  • 3.3.3.8. Coated sand
  • 3.3.3.9. Nanoparticles
  • 3.3.3.10. Laterite soil
  • 3.3.3.11. Portland cement
  • 3.3.3.12. Iron-based adsorbent
  • 3.3.3.13. Other adsorbents
  • 3.4. Synthesis of low-cost adsorbents for arsenic
  • 3.4.1. Partial thermal dehydration method
  • 3.4.1.1. Materials and procedures
  • 3.4.1.2. Equipment
  • 3.4.1.3. Measurement
  • 3.4.1.4. Synthesis procedure
  • 3.4.1.5. Determination of arsenic adsorption capacity of the active alumina
  • 3.4.1.6. Arsenic adsorption column
  • 3.4.1.7. Analytical procedures
  • 3.4.2. Effects of operating conditions on characteristics of the developed adsorbent
  • 3.4.2.1. Effect of temperature on surface area development
  • 3.4.2.2. Effect of residence time on surface area development
  • 3.4.2.3. Effect of rapid dehydration
  • 3.4.2.4. Effect of particle size
  • 3.4.2.5. Efficiency in removing arsenic from water
  • 3.4.3. Modeling and simulation of column adsorption for scale up
  • 3.4.3.1. Kinetics of adsorption and adsorption isotherm
  • 3.4.4. Dynamic modeling of adsorption in a fixed-bed column
  • 3.4.4.1. Breakthrough studies for model validation
  • 3.4.4.2. Error Analysis
  • 3.5. Technoeconomic feasibility analysis
  • Nomenclature
  • References
  • Chapter 4: Arsenic Removal by Membrane Filtration
  • 4.1. Introduction to arsenic removal by membranes
  • 4.2. Membrane filtration modes, modules, and materials in arsenic separation
  • 4.2.1. Concentration polarization and fouling of membrane surface
  • 4.2.2. Filtration Mode
  • 4.2.3. Membrane modules
  • 4.2.3.1. Plate and frame module
  • 4.2.3.2. Flat-sheet cross-flow module
  • 4.2.3.3. Spiral-wound module
  • 4.2.3.4. Hollow-fiber module
  • 4.2.3.5. Shell and tube or tubular module
  • 4.2.4. Membrane materials
  • 4.3. Low-pressure membrane filtration in arsenic removal
  • 4.4. High-pressure membrane filtration in arsenic removal
  • 4.4.1. Reverse osmosis in arsenic removal
  • 4.4.1.1. Mass transport through RO membrane
  • 4.4.1.2. Steady-state material balance for solute
  • 4.4.2. Arsenic removal by nanofiltration
  • 4.4.3. Filtration process in flat-sheet cross-flow module
  • 4.4.4. System performance measurement
  • 4.4.5. Flux behavior under varying transmembrane pressure
  • 4.4.6. Transmembrane pressure and rejection of arsenic
  • 4.4.7. Role of medium pH during nanofiltration of arsenic-contaminated water
  • 4.4.8. Iron in arsenic-contaminated water and its role in arsenic removal during nanofiltration
  • 4.5. Hybrid processes
  • 4.5.1. Adsorption integrated with ultrafiltration
  • 4.5.2. Coagulation-oxidation-membrane filtration
  • 4.5.3. Chemical oxidation integrated with flat-sheet cross-flow nanofiltration
  • 4.5.4. Chemical oxidation-nanofiltration integrated with chemical stabilization
  • 4.5.5. Nanofiltration/RO combined with chemical treatment
  • 4.5.6. Micro- and ultrafiltration with zerovalent iron or chemical precipitation
  • 4.5.7. Electro-ultrafiltration
  • 4.6. Chemical oxidation integrated with flat-sheet cross-flow nanofiltration
  • 4.6.1. Oxidation-nanofiltration principle
  • 4.6.2. Performance and limitation of arsenic oxidants
  • 4.6.2.1. Ozone (O3) as oxidant
  • 4.6.2.2. Hydrogen peroxide (H2O2)
  • 4.6.2.3. Chlorine (Cl2)
  • 4.6.2.4. Potassium permanganate
  • 4.6.3. The treatment plant
  • 4.6.4. Chemical oxidation-nanofiltration integrated with chemical stabilization
  • 4.6.4.1. A novel complete system of arsenic separation and stabilization
  • 4.6.4.2. Transport and stabilization principles
  • 4.6.4.3. Oxidation-nanofiltration-coagulation-integrated plant
  • 4.6.4.4. Preoxidation unit
  • 4.6.4.5. Nanofiltration unit in flat-sheet cross-flow module
  • 4.6.5. Performance of the Nanofiltration Module
  • 4.6.5.1. Pure water flux and rejection of arsenic and other contaminants
  • 4.6.5.2. Cross-Flow Rate and Flux Behaviour
  • 4.6.5.3. Stabilization Unit
  • 4.6.5.4. Optimization of stabilization process
  • 4.6.6. Assessment of stabilization
  • 4.6.6.1. Leaching tests for assessing stabilization of arsenic rejects (Ca-Fe-AsO4)
  • 4.6.6.2. Chemical analysis for assessing stabilization of arsenic rejects (Ca-Fe-AsO4)
  • 4.6.6.3. Structural Analysis
  • 4.7. Modeling and simulation of oxidation-nanofiltration hybrid process for scale up
  • 4.7.1. The principles
  • 4.7.2. Model equations
  • 4.7.2.1. Overall mass balance of aqueous solution in reactor unit
  • 4.7.2.2. Mass balance of As(V) in reactor unit
  • 4.7.2.3. Computation Procedure
  • 4.7.3. Determination of the model parameters
  • 4.7.3.1. Computation of flow rate and concentration of oxidant
  • 4.7.3.2. Computation of pore radius (rp) and effective membrane thickness (Deltax)
  • 4.7.3.3. Hindered diffusivity is calculated by [12]
  • 4.7.3.4. Computation of Peclet number by the Hagen-Poiseuille equation
  • 4.7.4. Governing parameters in preoxidation-nanofiltration process performance
  • 4.7.4.1. Oxidation dose and arsenic rejection
  • 4.7.4.2. Transmembrane pressure and rejection
  • 4.7.4.3. Transmembrane pressure and water flux
  • 4.7.4.4. Membrane charge density and arsenic rejection during nanofiltration
  • 4.8. Optimization and control of membrane-based plant operations
  • 4.8.1. ARRPA: The optimization and control software
  • 4.8.2. Software Description
  • 4.8.2.1. Data sheet design
  • 4.9. Technoeconomic feasibility analysis for scale up
  • 4.9.1. Membrane-integrated hybrid treatment plant: oxidation-nanofiltration system
  • 4.10. Conclusion
  • Nomenclature
  • References
  • Chapter 5: Arsenic Removal by Membrane Distillation
  • 5.1. Principles of Membrane Distillation
  • 5.2. Advantages of membrane distillation
  • 5.2.1. MD over conventional distillation
  • 5.2.3. MD over pressure-driven membrane processes
  • 5.2.3.1. Low operating temperature and hydrostatic pressure
  • 5.2.3.2. Solute rejection
  • 5.2.3.3. Membrane selectivity
  • 5.2.3.4. Membrane fouling
  • 5.2.4. Membrane distillation over osmotic membrane distillation (OMD)
  • 5.3. Limitations of membrane distillation
  • 5.4. Membrane materials
  • 5.4.1. Polyvinylidene fluoride
  • 5.4.2. Polytetrafluoroethylene
  • 5.4.3. Polypropylene
  • 5.4.4. Membrane characteristics
  • 5.4.4.1. Membrane pore size
  • 5.4.4.2. Membrane porosity and pore size distribution
  • 5.4.4.3. Membrane thickness and pore tortuosity
  • 5.4.4.4. Liquid entry pressure (LEP) and membrane wetting
  • 5.4.4.5. Liquid solid contact angle and liquid surface tension
  • 5.4.4.6. Fouling and scaling
  • 5.4.4.7. Permeate quality and membrane wetting
  • 5.5. Membrane Distillation Configurations
  • 5.5.1. Direct contact membrane distillation (DCMD)
  • 5.5.2. Air gap membrane distillation (AGMD)
  • 5.5.3. Sweeping gas membrane distillation (SGMD)
  • 5.5.4. Vacuum membrane distillation (VMD)
  • 5.5.5. VMD versus pervaporation
  • 5.5.6. Comparison between different MD configurations
  • 5.6. Basic design criteria of membrane modules and changes over time
  • 5.7. Heat transfer in membrane distillation
  • 5.7.1. Temperature polarization effect
  • 5.7.2. Heat transfer steps in the MD process
  • 5.7.3. Convective heat transfer in the feed boundary layer
  • 5.7.4. Heat transfer across the membrane
  • 5.7.5. Convective heat transfer in the permeate boundary layer
  • 5.7.6. Overall heat transfer coefficient (U) and temperature polarization coefficient (TPC)
  • 5.7.7. Estimation of the interfacial temperatures
  • 5.7.8. Evaporation efficiency
  • 5.8. Mass transfer in membrane distillation
  • 5.8.1. Mass transfer in the feed side
  • 5.8.2. A single volatile component feed
  • 5.8.3. Nonvolatile solute(s) with one volatile component
  • 5.8.4. Two volatile component feed
  • 5.8.4. Mass transfer in the permeate side
  • 5.8.5. Permeate side resistance in AGMD
  • 5.8.6. Permeate side resistance in DCMD
  • 5.8.7. Permeate side resistance in SGMD
  • 5.8.8. Permeate side resistance in VMD
  • 5.8.9. Mass transfer through the membrane pores
  • 5.8.10. Knudsen flow or free molecule flow
  • 5.8.11. Viscous or convective, or bulk or Poiseuille flow
  • 5.8.12. Ordinary (continuum) or molecular diffusion
  • 5.8.13. The Knudsen-molecular diffusion transition
  • 5.8.14. The Knudsen-Poiseuille transition
  • 5.8.14.1. The Knudsen-Poiseuille transition for single species MD system
  • 5.8.14.2. The Knudsen-Poiseuille transition in DCMD and VMD systems
  • 5.8.14.3. The molecular-Poiseuille transition
  • 5.8.14.4. The Knudsen-molecular-Poiseuille transition
  • 5.8.14.5. The membrane distillation coefficient versus temperature, membrane pore size, and transport mechanisms
  • 5.8.15. Determination of membrane characteristics: Gas permeation (GP) test
  • 5.9. Solar-driven membrane distillation in arsenic removal
  • 5.9.1. Introduction
  • 5.9.2. Solar heating loop
  • 5.9.3. Arsenic removal loop
  • 5.9.4. Operation of the membrane distillation module
  • 5.9.5. The operating conditions
  • 5.9.5.1. Effect of feed temperature on flux
  • 5.9.5.2. Effect of feed velocity on flux and feed outlet temperature
  • 5.9.5.3. Effect of distillate velocity on flux and distillate outlet temperature
  • 5.9.5.2. Effect of arsenic concentration on flux
  • 5.9.5.3. Flux enhancement in new flash vaporization design
  • 5.10. Modeling and simulation of a new flash vaporization module for scale up
  • 5.10.1. Introduction
  • 5.10.2. Theoretical background of model development
  • 5.10.3. Model development
  • 5.10.4. Solutions to the model equations
  • 5.10.5. Determination of physico-chemical parameters
  • 5.10.5.1. Diffusion coefficient
  • 5.10.5.2. Water vapor pressure
  • 5.10.5.3. Enthalpy of liquid and vapor
  • 5.10.5.4. Film transfer coefficients in the feed side (hf) and permeate side (hp)
  • 5.10.5.5. Membrane-feed (Tfm) and membrane-permeate (Tpm) interfacial temperatures
  • 5.10.5.6. Membrane interfacial temperatures for modified FVMD model
  • 5.10.6. Simulation
  • 5.10.6.1. Effect of feed temperature on flux and vapor pressure
  • 5.10.6.2. Effect of feed temperature on temperature polarization coefficient and vapor pressure polarization coefficient
  • 5.10.6.3. Effect of feed temperature on heat transfer coefficients and transport resistances
  • 5.11. Techno-economic feasibility of use of solar membrane distillation
  • Nomenclature
  • Greek letters
  • Subscripts
  • Superscripts
  • References
  • Chapter 6: Disposal of Concentrated Arsenic Rejects
  • 6.1. Introduction
  • 6.2. Classification of arsenic-bearing wastes generated in different treatment plants
  • 6.3. Arsenic waste disposal methods
  • 6.3.1. Dilution and dispersion through landfill
  • 6.3.2. Volatilization of arsenic by mixing with livestock waste
  • 6.3.3. Encapsulation or stabilization of the arsenic residuals
  • 6.3.4. Encapsulation or stabilization via cementation
  • 6.3.5. Encapsulation or stabilization via matrix compound formation
  • 6.3.6. Encapsulation or stabilization of arsenic residuals by industrial slags
  • 6.3.7. Encapsulation or stabilization of arsenic residuals by polymer compounds
  • 6.3.8. Encapsulation or stabilization of arsenic residuals by inorganic salts
  • 6.3.9. Reuse as construction materials
  • 6.3.10. Continuous removal of arsenic and stabilization: A novel approach
  • 6.4. Conclusion
  • References
  • Chapter 7: Arsenic Removal Technologies on Comparison Scale and Sustainability Issues
  • 7.1. Introduction
  • 7.2. Merits and demerits associated with broad arsenic abatement systems
  • 7.2.1. Membrane-based systems
  • 7.2.2. Adsorption-based process
  • 7.2.3. Chemical coagulation-precipitation
  • 7.2.3.1. Performance and limitation of arsenic oxidants
  • 7.2.3.2. Ozone (O3)
  • 7.2.3.3. Hydrogen peroxide (H2O2)
  • 7.2.3.4. Chlorine (Cl2)
  • 7.2.3.5. Potassium permanganate (KMnO4)
  • 7.3. Comparison of technologies in terms of arsenic removal efficiency
  • 7.4. Comparison of residual generation and disposal methods
  • 7.5. Overall qualitative comparison
  • 7.6. Toward sustainable solutions
  • 7.6.1. Selection of sustainable technology
  • 7.6.2. Selection and adoption of sustainable water management strategy
  • References
  • Index
Chapter 2

Chemical Treatment Methods in Arsenic Removal


Abstract


This chapter describes physico-chemical treatment of arsenic-contaminated groundwater. The forms of arsenic, the underlying principles of chemical coagulation, and precipitation and separation of arsenic from the aqueous phase, which are central to this arsenic removal technology, are elaborated in this chapter. Based on the theoretical understanding, mathematical modeling and simulation are done to help scale up the method for the practical field. Finally, development of software meant for optimization and control of the whole physico-chemical process is presented.

Keywords

Arsenic removal

chemical precipitation

destabilization

optimization and control

Contents

2.1 Different forms of arsenic in groundwater   26

2.2 Chemical precipitation   27

2.2.1 Alum precipitation   28

2.2.2 Lime softening   29

2.2.3 Iron precipitation   29

2.2.4 Enhanced coagulation   31

2.2.5 Coprecipitation   31

2.3 Physical separation   31

2.3.1 Diffuse-double-layer theory   32

2.3.2 Destabilization of colloids and settling of particles   34

2.3.2.1 Double layer compression   35

2.3.2.2 Adsorption and neutralization of charge   35

2.3.2.3 Enmeshment-precipitation   35

2.3.2.4 Interparticle bridging   35

2.3.3 Filtration   35

2.3.3.1 Rapid sand filtration   35

2.3.3.2 Backwashing   36

2.4 Modeling and simulation of the physico-chemical processes for scaleup   36

2.4.1 Introduction   36

2.4.2 Operation of the treatment plant   37

2.4.3 Measuring arsenic concentration in water   39

2.4.4 Computation of percentage removal of arsenic   39

2.4.5 Modeling and simulation of physico-chemical treatment process   40

2.4.5.1 Process kinetics and modeling basis   40

2.4.5.2 Modeling the process   41

2.4.5.3 Material balance for the oxidizer unit   42

2.4.5.4 Component mass balance of arsenic   43

2.4.5.5 Component mass balance of oxidant   43

2.4.5.6 Material balance of the coagulator and flocculator   43

2.4.5.7 Material balance for the sedimentation unit   44

2.4.5.8 Filtration unit   45

2.4.6 Determination of the model parameters   45

2.4.6.1 Computation of flow rate and concentration of oxidant   45

2.4.6.2 Computation of root mean square velocity gradient (G) in the coagulator/flocculator   46

2.4.6.3 Computation of average flock size (dQM) in the coagulator-flocculator unit   46

2.4.6.4 Computation of flow rate and concentration of coagulant   46

2.4.6.5 Determination of settling velocity and superficial velocity in sedimentation unit   47

2.4.6.6 Determination of the filtration pressure drops due to filter cake and filter medium   48

2.4.6.7 Effects of the operating parameters   48

2.4.6.8 Effect of pH   50

2.4.6.9 Effect of oxidant dose   51

2.4.6.10 Effect of coagulant dose   52

2.4.6.11 Effect of feed concentration   53

2.4.7 Performance of the system and the model   54

2.5 Optimization and control of treatment plant operations   55

2.5.1 Development of the optimization and control software   55

2.5.2 The overall procedure of computation and output generation   56

2.6 The numerical solution scheme and error monitoring   56

2.6.1 Software description   56

2.6.2 Software input   58

2.6.3 Software output   63

2.6.4 Running the software   63

2.6.4.1 Software analysis   63

2.7 Techno-economic feasibility analysis   65

Nomenclature   68

References   69

2.1 Different forms of arsenic in groundwater


Arsenic can occur in the environment in various forms and oxidation states (-3, 0, + 3, + 5) but in natural water, arsenic occurs mainly in inorganic forms such as oxyanions of trivalent arsenite or as pentavalent arsenate. The two oxidation states common in drinking water in the form of arsenate and arsenite are part of the arsenic (H3AsO4) and arseneous (H3AsO3) acid systems, respectively. These two forms depend upon oxidation-reduction potential and pH of the water. At typical pH values of 5.0-8.0 in natural waters, the predominant arsenate species are 2AsO4- and 42-, and the arsenite species is H3AsO3. Under oxidizing conditions, 42- dominates at a high pH regime, whereas H3AsO4 predominates at a low pH regime. 2AsO4- predominates at a low pH (< 6.9). This means that As(III) remains as a neutral molecule in natural water. Arsenates are stable under aerobic or oxidizing conditions, while arsenites are stable under anaerobic or mildly reducing conditions. In reducing waters, arsenic is found primarily in the trivalent oxidation state in the form of arseneous acid, which ionizes according to the following equations:

The acid base dissociation reactions of arsenic acid can be described as:

Surface water is also found to be contaminated with arsenic by the anthropogenic sources to various degrees since arsenic is also used in agriculture (pesticide), industrial applications, mining activities, and feed additives.

2.2 Chemical precipitation


Arsenic can be separated from aqueous solutions through chemical precipitation, exploiting the insolubility of some arsenic compounds. Most dominant arsenic compounds that are precipitated out in this way are arsenic sulphide, ferric arsenate, and calcium arsenate, where pH plays a very crucial role in such precipitation. In the neutral pH regimes, the inorganic arsenic compounds of Cu(II), Zn(II), Pb(II), and Fe(II) are more stable [1]. In chemical precipitation, the As(V) is the dominant form. Iron (II) arsenate [2] is highly insoluble and stable for its successful adoption [2]. A large number of calcium arsenate compounds can be very effectively precipitated out from aqueous solutions of As(V) by raising pH through the addition of lime. But compounds such as those precipitated out at a pH above 8 are often not very stable, particularly in the atmospheric carbon dioxide environment where soluble carbonates are easily formed. More complex arsenic compounds such as apatite structured calcium phosphate arsenate or ferric arsenite have been found to be more appropriate forms of arsenic precipitation and subsequent stabilization.

Chemical precipitation in general is considered to be a permanent, efficient, and easy-to- monitor method that can have immediate results. Simultaneous removal of many metal contaminants is possible with the chemical precipitation method. Chemical precipitation may be very useful for large-scale treatment of high-arsenic water, but is not suitable for deep elimination of arsenic up to the level...

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Tablet/Smartphone (Android; iOS): Installieren Sie bereits vor dem Download die kostenlose App Adobe Digital Editions (siehe E-Book Hilfe).

E-Book-Reader: Bookeen, Kobo, Pocketbook, Sony, Tolino u.v.a.m. (nicht Kindle)

Das Dateiformat PDF zeigt auf jeder Hardware eine Buchseite stets identisch an. Daher ist eine PDF auch für ein komplexes Layout geeignet, wie es bei Lehr- und Fachbüchern verwendet wird (Bilder, Tabellen, Spalten, Fußnoten). Bei kleinen Displays von E-Readern oder Smartphones sind PDF leider eher nervig, weil zu viel Scrollen notwendig ist. Mit Adobe-DRM wird hier ein "harter" Kopierschutz verwendet. Wenn die notwendigen Voraussetzungen nicht vorliegen, können Sie das E-Book leider nicht öffnen. Daher müssen Sie bereits vor dem Download Ihre Lese-Hardware vorbereiten.

Weitere Informationen finden Sie in unserer E-Book Hilfe.


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ePUB mit Adobe DRM
siehe Systemvoraussetzungen
PDF mit Adobe DRM
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Hinweis: Die Auswahl des von Ihnen gewünschten Dateiformats und des Kopierschutzes erfolgt erst im System des E-Book Anbieters
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